TISSUES OF THE BODY. 



393 



Fig. 394. Cuticle from the shaft ol the 

 human hair. One specimen shows the 

 medullary mass, the other not. 



clothed with a double layer of small pale nucleated cells (g). Taking the 

 hair higher up, we see the peripheral layer of these cells assuming more a 

 short thick figure, even after they have lost their nuclei. They extend 

 as far as the upper part of the follicle, where they terminate. From the 

 fact that they are frequently met with loosened from the hair and 

 clinging to the internal root-sheath, they have been regarded by some as 

 representing the cuticle of the latter. 



But the cells of the internal layer, which are not lost as we ascend, are 

 of greater importance. These remain fixed to the shaft throughout its 

 whole length, and communicate to it a peculiar transversely striated 

 appearance. The cells assume, at the upper portion of the bulb, a more 

 elongated form and a position more and more oblique as regards the 

 surface of the latter. Losing their nuclei and becoming more and more 

 flattened (fig. 392, /), they are gradually transformed into a series of 

 obliquely-placed thin and transparent scales (fig. 39 3, e,f) of -03 7 7-0 '0451 

 in diameter, which overlap each other like roofing tiles, the lower lying 

 with their free edges upon those above. 

 Thus originates that series of delicate 

 irregularly undulating or jagged lines 

 which are seen passing across the sur- 

 face of the fresh hair (fig. 394; and 

 392,/*/), connected in a reticular man- 

 ner with one another by means of other 

 obliquely coursing lines (1). We some- 

 times succeed in detecting these cells, 

 on the outline of the hair, owing to their 

 upper free edge projecting from the shaft 

 in the form of small ridges. To show them properly, we have recourse to 

 the action on the tissue of solutions of soda, or, better still, of sulphuric 

 acid. 



There still remains for consideration the axial or medullary mass of 

 the hair (2). This is, however, no essential constituent of the structure 

 in question, in that it is not to be found as a rule in downy hairs, and 

 is frequently absent in part or entirely in those of the head. It presents 

 itself in the form of a streak in the centre of the stem, occupying about a 

 fourth of the thickness of the latter (fig. 392, m, n; 394). 



Whilst at the boundary between the bulb and commencement of the 

 shaft the external cells become elongated, and the transformation into 

 the characteristic hair-plates commences, those situated internally assume 

 a more or less angular form as they become arranged in several layers and 

 increased in size until they may measure 0'0151-0'0226 mm. These 

 soon lose their nuclei and dry up (fig. 392, Tc). On the other hand, small 

 cavities are found in great number and most extensively in the contents 

 of the cells, which become filled with corresponding bubbles of air, pre- 

 senting, owing to their tiny proportion, the appearance of fatty or 

 pigmentary molecules (fig. 392), which they were long supposed to be. 

 They communicate to the medullary substance of white hair a silvery 

 appearance with reflected light, whilst in coloured hair, whatever be its 

 tint, the white axial portion shines through. By suitable treatment we 

 are able to expel the air from the medulla in the same manner as from a 

 thin section of bone, when, on subsequent drying, it rapidly fills again. 



REMARKS. On the upper edges of the cuticular cells becoming more everted the 

 transverse lines appear with greater distinctness. Hairs which have been torn out 



